A related-art pointing axis estimation apparatus can detect alignment variations caused by an optical axis of an optical system and an installation of a detection unit in an optical sensor by means of a plurality of laser light beams and light receiving elements for receiving the laser light beams, and can transmit the variations to a ground station, thereby correcting an image distortion caused by changes in an observation viewing direction (pointing direction) and optical performance, which are caused by random and short-term alignment variations in the optical sensor (for example, refer to Patent Literature 1).